This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This is an investigator-initiated open label phase II clinical trial examining the use of exemestane as a chemoprevention for breast cancer among high risk, post-menopausal women. High risk is defined as: history of stage I or II breast cancer 2 years out from definitive therapy;Gail model 5 year risk ? 1.7%;history of treated DCIS;history of high risk lesion on breast biopsy (ADH, ALH, LCIS);or known or suspected BRCA1 or BRCA2 mutation. The primary objective is to determine the effect of exemestane on mammographic density after one year of therapy. Secondary objectives include determining the effect of exemestane on: bone mineral density, breast tissue biomarkers (mammotome biopsy annually for 2 years is required;markers include TFF-1, PCNA, prolactin , prolactin receptor), and modulations of serum biomarkers (hormones, leptin, IGF components, lipids).